Post-translational modifications of histone proteins, such as methylation and acetylation, play an important role in the regulation of gene expression and other chromatin-associated processes. They may also be involved in various diseases such as autoimmune diseases, developmental disorders and cancer. To date, more than 100 histone modifications are known. They occur in complex patterns, forming the so-called “histone code”. With a view to deciphering this code and gain a better understanding of its role in human disease, the identification and characterisation of co-occurring histone modifications is an area of intense research.
The isolation of nucleosomes having multiple co-occurring histone modifications is used to detect the presence of co-occurring histone modifications. It also facilitates their further analysis. Nucleosomes having multiple-modified histone protein octamers can be isolated by consecutive chromatin immunoprecipitation (ChIP) assays: First, a ChIP assay using an antibody directed to a first histone modification is performed. The precipitated nucleosomes are then eluted and subjected to a second ChIP assay using an antibody directed to a second histone modification. Consecutive ChIP assays are not only time-consuming; they also require a lot of starting material and are technically difficult to perform. Moreover, consecutive ChIP assays have a poor sensitivity and the DNA recovered from the isolated nucleosomes cannot be analysed by next-generation sequencing to date.
Therefore, new tools and methods for isolating nucleosomes having multiple-modified histone protein octamers are needed that overcome the current limitations.